#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,c,i,j,prim[2000005];
int main()
{
    f>>n;
    for (i = 2; i <= n; i++)
        if (prim[i]==0)
        {
            c++;
            for (j = i+i; j <= n; j = j+i)
                prim[j] = 1;
        }
        g<<c;
    return 0;
}